In Central European countries, there’s a centuries-old practice, which is called Blaudruck (blue-dyeing) in Austria and Germany. It involves printing a paste called Papp onto cloth before dyeing over it with indigo, and was so significant to German culture that it’s influenced idioms (apparently the phrase “blue Monday” can be traced back to it). The craft almost disappeared in the 1980s. Here’s how a new generation revived it.
https://www.bbc.com/travel/article/20230420-blaudruck-europes-secret-dyeing-formula